Conventionally, a direct conversion type radiation detector which converts radiation directly into carriers (charge information) in a semiconductor layer applies a predetermined bias voltage to a common electrode formed on a front surface of the semiconductor layer which is sensitive to radiation, and collects the carriers thereby generated in the semiconductor layer in pixel electrodes formed on a back surface of the semiconductor layer. Further, the carriers collected are taken out as radiation detection signals, thereby to detect the radiation.
Where an amorphous semiconductor layer such as a-Se (amorphous selenium), in particular, is used as the radiation sensitive semiconductor layer, a large and thick semiconductor layer can be formed easily by a method such as vacuum vapor deposition. Thus, the amorphous semiconductor layer can be constructed as a radiation conversion layer of a two-dimensional array type radiation detector.
However, since the direct conversion type radiation detector applies a high voltage to the common electrode for use, there arise problems of dark current increase and creeping discharge. Further, the radiation detector having the larger area is the more likely to encounter a problem of warpage and cracking due to temperature change. First, in Patent Document 1 and in FIG. 6, a carrier selective high resistance film 5 is inserted between a common electrode 3 and a semiconductor layer 1 as a measure to reduce dark current. In order to solve the problem of creeping discharge, a curable synthetic resin film 7 (silicone resin) as an insulating layer of high withstand voltage covers entire surfaces of the amorphous semiconductor layer 1, carrier selective high resistance film 5 and common electrode 3. With this structure, however, temperature change will cause warpage of the radiation detector, and form cracks in the curable synthetic resin film 7, amorphous semiconductor layer 1, common electrode 3 and/or carrier selective high resistance film 5. A creeping discharge voltage resistance will become insufficient.
So, in Patent Document 2 and in FIG. 7, to prevent warpage and cracking from occurring with the radiation detector, an auxiliary plate 9 with a thermal expansion coefficient comparable to that of an insulating substrate 11 is fixed to pinch the curable synthetic resin film 7 of high withstand voltage with the insulating substrate 11. When silicone resin is used as the curable synthetic resin film 7 here, since silicone resin is inferior in hardness, warpage by thermal contraction of the radiation detector cannot be inhibited, but cracking will occur with the amorphous semiconductor layer 1, common electrode 3 and carrier selective high resistance film 5. For the above reason, an epoxy resin is used as the curable synthetic resin film 7 in Patent Document 2.
However, Patent Document 2 indicates a problem that the solvent component of the epoxy resin reacts with a-Se which is the amorphous semiconductor layer 1, to discolor the surface of the amorphous semiconductor layer 1 and to lower the withstand voltage. So, in Patent Document 2 and in FIG. 7, the high resistance film 5 such as Sb2S3 film having solvent resistance and carrier selectivity covers the entire surface of the amorphous semiconductor layer 1. This reduces the reaction between the solvent component of epoxy resin and a-Se, thereby to eliminate discoloring of the surface of the amorphous semiconductor layer 1 and lowering of the withstand voltage.
In Patent Document 3, a silane compound is used as the curable synthetic resin film 7 as a solution to the problem of warpage and cracking. This can make the thermal expansion coefficient of a mold material, itself, which consists of a silane compound, the same as that of the insulating substrate, whereby warpage and cracking can be inhibited without using the auxiliary plate 9.    [Patent Document 1]    Unexamined Patent Publication No. 2002-009268    [Patent Document 2]    Unexamined Patent Publication No. 2002-311144    [Patent Document 3]    Unexamined Patent Publication No. 2002-116259